In a silicon solar cell (photovoltaic device), unevenness referred to as a texture is provided on a light-receiving surface of a silicon substrate so as to prevent reflection of incident light and leakage of light trapped on the silicon substrate. A surface of a silicon substrate is usually textured by a wet process using an alkaline (KOH) solution as an etchant (see PTL 1, PTL 2, PTL 3, and PTL 4). The texturing by a wet process requires post-processes such as a cleaning process using hydrogen fluoride and a thermal process. Not only may the post-processes contaminate a surface of a silicon substrate, but they also have a disadvantage with regard to increased cost.
In addition, the wet process only allows texturing a silicon substrate having orientation (100) (see PTL 5, for example), and the wet process cannot form a texture on a surface of a silicon substrate having another orientation.
Techniques for forming a texture on a surface of a silicon substrate by a dry process have also been proposed. For example, 1) a technique using reactive ion etching by plasma (see PTL 6 and PTL 7), 2) a technique for etching by a photo-electrolysis reaction (PTL 8), and 3) a technique for etching a surface of a silicon substrate by introducing ClF3 gas and others into a reaction chamber in which the silicon substrate is placed (see PTL 9, PTL 10, and PTL 11) have been proposed.